Centrifugal compressor diffuser

ABSTRACT

The diffuser of a centrifugal compressor having an unshrouded rotor has boundary layer fences on the walls bounding the diffuser in advance of the diffuser vanes. These vanes are directed across the direction of flow of boundary layer air on the diffuser wall and curve into the direction of the diffuser vanes as they merge with the leading edge of the vanes.

United StatesPatent [191 Bandukwalla CENTRIFUGAL COMPRESSOR DIFFUSER [75] Inventor: Phiroze Bandukwalla,Indianapolis,

Ind.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[221 Filed:

21 Appl. No.: 188,133

[52] US. Cl 415/211, 4l5/D1G. 1, 415/143 [51] Int. Cl. F04d 29/44, F04d 17/60 [58] Field of Search 415/D1G. 1, 207,

[56] References Cited UNITED STATES PATENTS 2,967,013 1/1961 Dallenbach et al. 415/181 [451 Dec. 25, 1973 FOREIGN PATENTS OR APPLICATIONS 579,770 8/1946 Great Britain 415/211 Primary Examiner-Henry F. Raduazo Attorney-Paul Fitzpatrick et al.

[57] ABSTRACT The diffuser of a centrifugal compressor having an unshrouded rotor has boundary layer fences on the walls bounding the diffuser in advance of the diffuser vanes. These vanes are directed across the direction of flow of boundary layer air on the diffuser wall and curve into the direction of the diffuser vanes as they merge with the leading edge of the vanes.

3 Claims, 3 Drawing Figures CENTRIFUGAL COMPRESSOR DIFFUSER The invention described and claimed herein was conceived in the course of work under a contract with the Department of Defense.

My invention is directedto centrifugal compressors, and specifically to improvements in the diffusers of such compressors to energize boundary layer air in the diffuser and improve flow conditions in the diffuser.

Centrifugal compressors for air and other gases are very well known and widely employed and have great advantages, particularly in lower pressure ranges, because of the simplicity of their structure as compared to axial-flow compressors.

Such a compressor is described in Atkinson U.S. Pat. No. 2,819,012 for Centrifugal Compressor, Jan. 7, 1-958. Air enters the compressor through an annular entrance generally parallel to the axis of rotation and is accelerated circumferentially of the rotor while moving radially outward under the influence of centrifugal force, the discharge of air from the impeller being primarily tangential, with a substantial radial component and ordinarily little axial component of velocity.

The high velocity discharge from the rotor or impeller is diffused in structure providing a diverging flow path and the dynamic'head is thus in large measure converted to pressure head, so that the discharge is at a substantial rise in pressure above atmospheric or other inlet pressure. Such compressors are found in gas turbine engines, turbochargers, air conditioning machines, and various other environments.

In centrifugal compressors, as in other fluid dynamic machines, particularly in compressors, there is a natural' tendency for a build-up of more or less stagnant boundary layer air along the surfaces which define the passages through which the air or other gas flows. One result of such a boundary layer build-up is increased non-uniformity of velocity of flow through the passages. For most efficient diffusion of the flow passing from the compressor rotor into the diffuser, it is important that the gas flow be as nearly uniform as feasible, and that stagnant boundary layers be eliminated or minimized.

In the usual centrifugal compressor having an unshrouded rotor; that is, one in which the forward or outer boundary of the'flow path through the rotor is defined by a fixed case, the boundary layer adjacent this wall has relatively low absolute circumferential velocity. On the other hand, the boundary layer on the disk of the rotor or impeller which is rotating at high velocity is carried with the impeller and thus has a high absolute circumferential velocity.

There has been recognition of the boundary layer or uneven flow problem in diffusers; see, for example, US. patents to Browne No. 2,372,880, Apr. 3, 1945, and to Dallenbach et al. No. 2,967,013, .Ian. 3, 1961.

My invention involves the provision of small ridges termed boundary layer fences so disposed as to energize the boundary layer air by mixture with the main flow of air from the impeller.

The provision of boundary layer fences and the reasons for their use are previously known; see, for example, Barney et al. US. Pat. No. 3,014,640, Dec. 26, 1961, in which boundary layer fences are applied to airfoils to promote energization of the boundary layer air and mixture with the main stream flowing past the airfoil. However, I am not aware of the application of boundary layer fences as in my invention.

The principal objects of my invention are to improve the performance of centrifugal compressors, to improve the flow in centrifugal compressor diffusers, and to provide boundary layer fence arrangements in centrifugal compressors particularly adapted to minimize the boundary layer on the walls defining the diffuser.

The nature of my invention and its advantages will be apparent to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention and the accompanying drawings.

FIG. 1 is a sectional view of a centrifugal compressor taken on a plane containing the axis of rotation.

FIG. 2 is a partial transverse sectional view taken on the plane indicated by the line 22 in FIG. 1.

FIG. 3 is a partial transverse sectional view taken on the plane indicated bythe line 33 in FIG. 1.

Referring first to FIG. 1, the centrifugal compressor, illustrated more or less schematically, comprises a housing 2 having a front wall 3 and a rear wall 4. A rotor or impeller 6 disposed between the walls is suitably fixed to a shaft 7. The shaft is rotatably supported in a bushing 8 mounted in a bearing support 10 suitably supported from the front wall and in a bushing 11 mounted in the rear wall 4. The front wall 3 and hearing support 10 define an annular air entrance or eye 12. The front and rear walls define between them a diffuser 14, only the inner part of which is illustrated.

The rotor 6 comprises a hub or disk 15 fixed on shaft 7. The hub defines the inner and rear boundary of the gas flow path through the compressor rotor. The front wall 3 defines the outer and forward boundary of this flow path.

The air is moved by a ring of generally radially extending blades 16, the initial portions of which are curved forwardly to act as the inducer portion of the impeller and the rear or radially outer portions of which lie approximately or exactly in surfaces parallel to the axis of the shaft 7. The blades terminate at a tip 18 which may be at the same radius as the periphery of the disk 15. The structure so far described is known, and may be the same as that described at greater length in the aforementioned Atkinson patent.

The difiuser 14 is of annular structure bounded at the front by wall 3 and at the rear by wall 4. Curved vanes 19, only the radially inner portion of which is illustrated, serve to guide and direct flow as the passage area increases and velocity decreases in the flow through the diffuser. Between the tips 18 of the rotor blades 16 and the leading edges 20 of the diffuser vanes there is an annular vaneless diffusing space 22. The boundary layer fences which are the subject matter of my invention are disposed on the inner surfaces of walls 3 and 4 within this vaneless space. Except for the provision of these fences, the diffuser, including the vanes, may be similar to that described in Conklin et al. US. Pat. No. 3,027,717, Apr. 3, 1962.

Considering the boundary layer fences, with particular reference also to FIGS. 2 and 3, it may be borne in mind that in FIG. 2 the impeller appears as rotating clockwise and, as viewed in FIG. 3, it is rotating counterclockwise. FIG. 2 illustrates the boundary layer fences 24 on what may be termed the disk or hub side of the diffuser, this being the side which is aligned with the disk 15 of the impeller. Since, as previously stated, the boundary layer air discharged along the surface of the disk 15 is discharged primarily tangentially, as indicated by the arrow 26 in FIG. 2, the boundary layer fences are disposed generally radially to lie across such boundary layer flow and thus to divert the boundary layer from the surface into the main flow and also, to some extent, to redirect the flow. As will be seen from the arrow 26 the generally tangential boundary layer flow will strike the radially inner portion of one of the fences 24 which will serve to energize the boundary layer. The radially outer portions of these fences curve as illustrated so as to fair into or trend in the same direction as the leading portion of vanes 19 of the diffuser.

FIG. 3 illustrates what may be termed shroudfences 28, the term being applied because the flow for which these fences are provided is the flow which is limited in circumferential velocity by its flow along the fixed shroud defined by the forward wall 3 of the compressor housing. The general direction of this flow is primarily radial, as indicated by the arrow 30 in FIG. 3. The fences 28 are disposed tangentially so that the air flowing primarily radially outward is intercepted by the fences and diverted into the main air stream. Because of the difference in the direction of the fences, the fences 28 originate farther from the tips 18 of the blades than the fences 24.

Incidentally, it may be pointed out that in some compressors the impeller includes a rotating shroud which moves with the blades 16 and lies immediately inside the forward wall 3. With a device of this sort, the flow from both sides of the impeller would be similar to that described for the hub side in this case and, therefore, the fences on both faces of the diffuser would be similar to fences 24.

The fences are of very small size, such as about 0.050 inch in height. They may have a triangular or rectangular cross section, the cross section not being critical. The roughness of the surface over which the boundary layer flows is not critically affected by the exact cross section of the protruding fences.

It may be desirable to have the height of the fence, the distance of its projection from the wall, increase slightly in the radially outward direction. It is best to provide a gradual transition at the leading edge of tbe diffuser vanes from the fence as indicated by the are 32 (FIG. 1) at the terminus of fences 24 and a similar arc illustrated at the terminus of fences 28.

By energizing the sluggish boundary layer air and mixing it with the main flow through the diffuser, the uniformity of flow and thus the angle of attack of flow to the diffuser vanes is improved. As a result, compressor efficiency is improved.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

I claim:

1. A centrifugal compressor comprising, in combination, a rotor including a disk having a generally radial face defining one boundary of the flow path through the rotor and blades extending axially of the rotor from one face of the disk and the flow from the rotor being substantially tangentially therefrom, a stator defining the other boundary of the flow path through the rotor, and a diffuser having two generally radial stationary walls providing continuations of the said boundaries,

the diffuser including vanes bridging the space between the said walls and spaced radially from the rotor blades by a vaneless space, the diffuser being characterized by boundary layer fences extending from both of said walls into the diffuser, each said fence having an end nearest the rotor disposed across the direction of boundary layer flow from tbe rotor along the said one wall, and each fence curving gradually into a terminal portion fairing into the leading edge of one of said vanes; the fences on the wall continuing the disk boundary having initial portions trending primarily radially and the fences on the wall continuing the stator boundary having initial portions trending primarily tangentially with respect to the rotor axis.

2. A centrifugal compressor comprising, in combination, a rotor including a disk having a generally radial face defining one boundary of the flow path through the rotor and blades extending axially of the rotor from one face of the disk and the flow from the rotor being substantially tangentially therefrom, a stator defining the other boundary of the flow path through the rotor, and a diffuser having two generally radial stationary walls providing continuations of the said boundaries, the diffuser including vanes bridging the space between the said walls and spaced radially from the rotor blades by a vaneless space, the diffuser being characterized by boundary layer fences extending from both of said walls into the diffuser, each said fence having an end nearest the rotor disposed across the direction of boundary layer flow from the rotor along the said one wall, and each fence curving gradually into a terminal portion fairing into the leading edge of one of said vanes; the fences on the wall continuing the disk boundary having initial portions beginning near the rotor trending primarily radially from the rotor and having a concave curvature into the vanes as viewed from the rotor; and the fences on the wall continuing the stator boundary beginning farther from the rotor and having initial portions trending primarily tangentially with respect to the rotor and having a convex curvature into the vanes as viewed from the rotor.

3. A centrifugal compressor comprising, in combination, a rotor including a disk having a generally radial face defining one boundary of the flow path through the rotor and blades extending axially of the rotor from one face of the disk and the flow from the rotor being substantially tangentially therefrom, means defining the other boundary of the flow path through the'rotor, and a diffuser having two generally radial stationary walls providing continuations of the said boundaries, the diffuser including vanes bridging the space between the said walls and spaced radially from the rotor blades by a vaneless space and extending substantially tangential relative to the periphery of the rotor, the diffuser being characterized by boundary layer fences extending into the diffuser from the wall continuing the disk boundary, each said fence having an end near to the rotor and an initial portion trending primarily radially from the rotor from the said end across the direction of boundary layer flow from the rotor along the said wall, and each fence curving gradually into a terminal portion fairing into the leading edge of one of said vanes with a curvature which is concave as viewed from the rotor. 

1. A centrifugal compressor comprising, in combination, a rotor including a disk having a generally radial face defining one boundary of the flow path through the rotor and blades extending axially of the rotor from one face of the disk and the flow from the rotor being substantially tangentially therefrom, a stator defining the other boundary of the flow path through the rotor, and a diffuser having two generally radial stationary walls providing continuations of the said boundaries, the diffuser including vanes bridging the space between the said walls and spaced radially from the rotor blades by a vaneless space, the diffuser being characterized by boundary layer fences extending from both of said walls into the diffuser, each said fence having an end nearest the rotor disposed across the direction of boundary layer flow from tbe rotor along the said one wall, and each fence curving gradually into a terminal portion fairing into the leading edge of one of said vanes; the fences on the wall continuing the disk boundary having initial portions trending primarily radially and the fences on the wall continuing the stator boundary having initial portions trending primarily tangentially with Respect to the rotor axis.
 2. A centrifugal compressor comprising, in combination, a rotor including a disk having a generally radial face defining one boundary of the flow path through the rotor and blades extending axially of the rotor from one face of the disk and the flow from the rotor being substantially tangentially therefrom, a stator defining the other boundary of the flow path through the rotor, and a diffuser having two generally radial stationary walls providing continuations of the said boundaries, the diffuser including vanes bridging the space between the said walls and spaced radially from the rotor blades by a vaneless space, the diffuser being characterized by boundary layer fences extending from both of said walls into the diffuser, each said fence having an end nearest the rotor disposed across the direction of boundary layer flow from the rotor along the said one wall, and each fence curving gradually into a terminal portion fairing into the leading edge of one of said vanes; the fences on the wall continuing the disk boundary having initial portions beginning near the rotor trending primarily radially from the rotor and having a concave curvature into the vanes as viewed from the rotor; and the fences on the wall continuing the stator boundary beginning farther from the rotor and having initial portions trending primarily tangentially with respect to the rotor and having a convex curvature into the vanes as viewed from the rotor.
 3. A centrifugal compressor comprising, in combination, a rotor including a disk having a generally radial face defining one boundary of the flow path through the rotor and blades extending axially of the rotor from one face of the disk and the flow from the rotor being substantially tangentially therefrom, means defining the other boundary of the flow path through the rotor, and a diffuser having two generally radial stationary walls providing continuations of the said boundaries, the diffuser including vanes bridging the space between the said walls and spaced radially from the rotor blades by a vaneless space and extending substantially tangential relative to the periphery of the rotor, the diffuser being characterized by boundary layer fences extending into the diffuser from the wall continuing the disk boundary, each said fence having an end near to the rotor and an initial portion trending primarily radially from the rotor from the said end across the direction of boundary layer flow from the rotor along the said wall, and each fence curving gradually into a terminal portion fairing into the leading edge of one of said vanes with a curvature which is concave as viewed from the rotor. 